School of Biological Sciences

The University of Hong Kong

M.L. Chye, the Wilson and Amelia Wong Professor in Plant Biotechnology at HKU, completed her PhD on a Commonwealth Scholarship at the University of Melbourne and received postdoctoral training in Plant Molecular Biology at the Rockefeller University (New York) and the Institute of Molecular and Cell Biology (Singapore). She joined the University of Hong Kong in 1993 was promoted to Professor in 2005.

She has been awarded an Edward Clarence Dyason Universitas 21 Fellowship (2004/05), an Outstanding University Researcher Award (2006/07), a Croucher Senior Research Fellowship (2007/08), and an Eileen Mary Harris Scholarship (2013). She serves on the editorial boards of Plant Molecular Biology (Springer), Planta (Springer), Frontiers in Plant Metabolism & Chemodiversity, Frontiers in Plant Cell Biology, and Frontiers in Plant Physiology, was Chair of the 4th Asian Symposium on Plant Lipids (2011) and Chair of the 12th International Symposium on Biocatalysis and Agricultural Biotechnology (2016).

Laboratory of Plant Molecular Biology

Research Team

Research Interests

The main focus of the Chye Lab is to understand the function and mechanism of action of stress-induced plant proteins, particularly plant acyl-CoA-binding proteins (ACBPs). We intend to use them to generate transformed plants that can better tolerate abiotic and biotic stresses since these stresses account for ~40 % loss in crop productivity. Ultimately, investigations on plant ACBPs, and others, will be applied to agriculture and phytoremediation.

Arabidopsis acyl-CoA-binding proteins (ACBPs) and stress tolerance

We are studying a family of plant ACBPs which bind acyl-CoA esters and transport them within the plant cell. In Arabidopsis and rice, six genes encode four structurally distinct classes of ACBPs (Leung et al., 2004; Xiao and Chye, 2009; 2011b; Meng et al., 2010; 2014). In Arabidopsis the six members are

10-kDa cytosolic ACBP of which homologues have been well-characterized in other eukaryotes (Chen et al., 2008),

Stress-inducible HMGS, an enzyme in plant isoprenoid metabolism

We are investigating the role of 3-hydroxy-3-methylglutaryl-CoA synthase (HMGS) in plant isoprenoid metabolism. HMGS is an enzyme in the cytosolic mevalonate pathway which produces sterols, sesquiterpenes and polyterpenes. Its expression is stress-inducible and is highest during early development in flower, seed and seedling (Alex et al., 1999). Four isogenes encoding HMGS are differentially expressed in Brassica juncea (Nagegowda et al., 2005).

Using green fluorescent protein fusions, B. juncea HMGS1 (BjHMGS) has been subcellularly localized to the cytosol (Nagegowda et al., 2005). We have biochemically purified and characterized His-tagged recombinant BjHMGS expressed in Escherichia coli, presenting a first detailed characterization of a plant HMGS, and the amino acids involved in catalysis were identified by site-directed mutagenesis (Nagegowda et al., 2004). In collaboration with the Bach Lab and the Noel Lab, the crystal structure of Brassica HMGS covalently bound to specific inhibitor F-244 has been determined, providing a first approach towards the design of more potent cholesterol-lowering drugs and antibiotics that target the mevalonate pathway (Pojer et al., 2006).

When mutant and wild-type BjHMGS were expressed in transgenic Arabidopsis, the genes of the sterol biosynthetic pathway were upregulated resulting in an overaccumulation of phytosterols (stimasterols, campesterol and stigmasterols), and the HMGS-overexpressing lines were better protected against oxidative stress and Botrytis infection (Wang et al., 2012). Furthermore, the overexpression of HMGS variant S359A in a model plant from the family Solanaceae, not only resulted in phytosterol accumulation but showed enhanced plant growth, pod size and seed yield (Liao et al., 2014; US Patent Application 14/260,561). The potential of S359A in boosting seed yield may now be tested in food crops.

Expression of siRNAs and heterologous proteins in genetically-transformed plants

Some of the strategies currently used to engineer crops to stress tolerance exploit the natural mechanisms used by the plant. We have isolated defense-related genes from tropical plants for expression in transgenic crops. To this end, we have cloned and characterized cDNAs encoding beta-1, 3-glucanase from Hevea brasiliensis (Chye and Cheung, 1995, Plant Mol Biol 29: 347-402) and an unusual Brassica juncea chitinase with two chitin-binding domains, designated BjCHI1 (Zhao and Chye, 1999; Fung et al., 2002). Potato transgenic for both proteins was protected from Rhizoctonia solani invasion (Chye et al., 2005). Besides displaying anti-fungal properties, BjCHI1 with its two chitin-binding domains can agglutinate Gram-negative bacteria (Tang et al., 2004; Guan et al., 2008). BjCHI1-susceptible fungal and bacterial phytopathogens have been identified for future applications in agriculture (Guan et al., 2008; Guan and Chye, 2008; US Patent No. 6,956,147). To better understand the function of plant chitinases in catalysis, we have examined their crystal structures with the Mowbray Lab (Ubhayasekara et al., 2007; 2009).

Research on proteinase inhibitor protein SaPIN2a from a weed, Solanum americanum (Xu et al., 2001), has not only led to the production of transgenic lettuce that are insect-resistant but that also show inhibition of endogenous trypsin- and chymotrysin-like activities (Xu et al., 2004). Thus, SaPIN2a can be used to protect heterologously expressed proteins by minimizing protein degradation and optimizing protein yield in transgenic plant bioreactors (US Patent No. 7,256,327). SaPIN2a and SaPIN2b function endogenously by inhibiting proteinase activities in phloem and floral development (Xu et al., 2001; Sin and Chye, 2004). We have used RNAi-based gene silencing to show that SaPIN2a and SaPIN2b are essential for seed development (Sin et al., 2006). A reduction in seed set was observed in PIN2-RNAi transgenic S. americanum lines; aborted seeds in transgenic fruits had an abnormal endothelium, suggesting that the endothelium allows proper endosperm and embryo formation through its ability to produce a proteinase inhibitor (Sin et al., 2006).

In other projects related to plant biotechnology, we have explored the use of transgenic plants as bioreactors by the characterization of promoters that direct expression in seeds (Chen et al., 2013), and the production of vaccines using nuclear transformation and plastid transformation (Zhou et al., 2006; Lee et al., 2006; Li et al., 2006; Li and Chye, 2009; Chye et al., Chinese Patent No. zl200480039355.6).